1. Field of the Invention
The present invention relates generally to a plank which in a single horizontal orientation forms a loading surface of a picnic bench, bleacher, boat dock and the like and, more particularly, to a plank with a primary structural element and load surface formed of a synthetic resin and a number of reinforcing bars preferably formed of a metal.
2. Discussion of Prior Art
It is known to provide wooden or metal planks for benches and the like with a thermoplastic cap or sheathing for enhancing the planks weatherability and life span. In this apparatus the wood or metal plank is the structural member and the thermoplastic cap or sheathing is merely a weather protectant and load surface cover--similar to a protective coating such as paint.
Conventionally, planks not employing thermoplastic covers use a wood stringer or metal beam that is treated or coated. Typically, wood stringers are constructed of a treated wood or coated with a protective paint. Metal beams are usually constructed of a non-corrosive metal such as aluminum, or a steel which is galvanized, plated, or painted with a rust inhibiting coating.
These initial plank constructions have the following shortcomings. Wood stringers are often characterized as having short lives with high maintenance costs. Wood stringers coated with paint often cause peeling, cracking, and ultimately destruction of the coatings due to exchange of moisture to and from the stringer. Treated wood contains chemicals which could be transferred to an individual by a splinter sometimes causing severe irritation.
Metal planks have also proven to be inadequate. A metal plank may not be quite as short-lived as a wood plank but is substantially more expensive and conducts heat away from the body. Aluminum, the most expensive metal alternative, tends to become burred after use and stains clothing if not properly anodized. Galvanized or plated steel often requires finishing to remove sharp excess coating material and additional machining. Painted steel requires regular maintenance or the beam rusts and poses a serious health risk (i.e. tetanus) to people using the plank. All of the above-mentioned plank materials demand some form of maintenance and, more importantly, most eventually require replacement at a considerable cost.
Thermoplastic covers are utilized to provide a safe, comfortable load surface and overcome the poor weatherability of wood stringers and metal beams, thus reducing the maintenance and replacement costs. By shielding surfaces exposed to sunlight and rain, the beam or stringer experiences only the detriments caused by changing temperature and humidity of the ambient air. Additionally, by covering the stringer or beam with a thermoplastic cover typical loading surface preparation, such as sanding, is eliminated. Improvements have also been made to the thermoplastic materials used in production and designs of the caps or sheathing. For example, designs of covers for wooden stringers have been modified to leave the undersurface exposed so the wood could "breathe" and adjust to ambient humidity changes.
Although the thermoplastic caps or sheathing represent an improvement over other conventional planks for a picnic bench and the like, there is a need to provide an improved plank which entirely eliminates costly wood stringers and metal beams. The use of a thermoplastic cover may reduce replacement and maintenance costs of planks, however, there is no diminution of initial construction costs. Clearly, initial costs are higher with the thermoplastic covers. Furthermore, utilizing thermoplastic covers only delays the replacement of the wooden stringers or metal beams and the considerable costs associated therewith.